High quality early care and education (ECE) experiences are critical for young children from birth to three, as they provide the foundation for future school success. However, there is national concern that classroom quality is low in toddler classrooms, particularly within early childhood programs serving children from low-income backgrounds. National policy initiatives, including Early Head Start (EHS) and Quality Rating and Improvement Systems (QRIS), have recently responded to this national need. Federal and local funding through these programs has increased substantially to support the improvement of classroom quality in ECE settings. To improve quality, assessments of classroom process quality that include the quality of teacher-child interactions are used. The Toddler Classroom Assessment Scoring System (CLASS-T) is one of the most commonly used measures to assess process quality in toddler classrooms within EHS and QRIS. In addition, cut-points on the CLASS-T contribute to programs being rated as high or low quality in QRIS. Programs? QRIS ratings have policy implications for program funding and for parent consumers. Despite widespread use of the CLASS-T for these purposes, few studies have examined the construct validity of the CLASS-T for use in EHS and subsidized child care programs serving low-income, ethnically and linguistically diverse children and families. In addition, no studies to date have empirically validated the a priori cut-points that QRIS use in practice. Research is needed to identify the point at which increases in classroom process quality contribute to children?s? developmental outcomes within programs serving diverse, low-income families. The proposed dissertation project will address these gaps in the field by first validating the CLASS-T in a sample of classrooms comprised of ethnically and linguistically diverse toddlers attending EHS and subsidized child care programs. Then, associations between CLASS-T domains and child outcomes will be examined. Finally, the cut-points that are currently in use as part of the local Miami-Dade County QRIS, Quality Counts, will be examined empirically to determine whether the a priori cut-points used in practice identify thresholds of classroom quality that are differentially associated with toddler language and social-emotional outcomes. The findings of the proposed project will be shared with local partners and implications for policy and practice will be discussed. Resources will be co-constructed in collaboration with local partners and shared with program staff to support quality improvement efforts.